1. Field of the Invention
The present invention relates to the field of digital signal receiving and processing systems and is intended for estimating the current signal-to-noise ratio.
2. Description of the Related Art
Estimation of a current signal-to-noise ratio at the input of the receiving device is relevant for communication and positioning radio systems and has been long the subject of engineering developments.
There are known methods and devices of estimating current signal-to-noise ratio described, for example, in patents and publications: U.S. Pat. No. 7,190,741, U.S. Pat. No. 8,368,593, U.S. Pat. No. 6,317,456, U.S. Pat. No. 8,495,480, U.S. Pat. No. 6,717,976, U.S. Pat. No. 7,032,160, U.S. Pat. No. 8,194,558, RU 2332676, RU 2414718, RU 2472167, RU 2429496, RU 2434325, RU 2446448, CN 1661996A, CN 101030787A, CN 101552752B, EP 2050214A2, as well as in patent applications: US2 0070168407, US 20070168407, US 20110188561, WO 2003085845, and so on.
U.S. Pat. No. 7,190,741, entitled “Real-Time Signal-to-Noise Ratio (SNR) Estimation for BPSK and QPSK Modulation Using the Active Communication Channel”, describes a method and device for measuring the current signal-to-noise ratio for BPSK and QPSK signals. The described device includes a quadrature mixer and a unit of estimating signal-to-noise ratio. The signal-to-noise ratio is determined on the basis of measuring the angle oscillation of the vector describing the received signal.
A method of measuring signal-to-noise ratio in U.S. Pat. No. 6,317,456 includes the operations of mean, square-rooting and dividing being performed with quadrature components of the received signal. But it is intended for OFDM-modulated signals.
US Patent Publication No. 20070168407 proposes a method of measuring signal-to-noise ratio with the help of filters, which is based on a difference in spectra of the desired signal and interference; the method comprises operations of filtering, square-rooting and taking a mean (integrating) for quadrature components of the received signal.
A method of estimating small changes in values of the signal-to-noise ratio presented in WO2003085845 suggests calculating the vector length of the received signal and determining its statistical characteristics, based on which the signal-to-noise ratio is further defined.
Patent RU2472167, entitled “Digital measurer of signal and interference strength in the passband of the receiver channel in real time”, describes a mixer, a band filter, ADC, multipliers, mean units, storing registers, etc. This reference describes two measuring channels: in the first channel, there is coherent processing, and in the second channel, there is incoherent processing of the received signal. However, this device does not process quadrature components of the received signal.
A method and device of estimating signal-to-noise ratio for BPSK and QPSK signals according to U.S. Pat. No. 7,190,741, entitled “Real-Time Signal-to-Noise Ratio (SNR) Estimation for BPSK and QPSK Modulation Using the Active Communication Channel”, includes a separation of quadrature components of the complex envelope of the received signal, calculation of a deviation/offset angle from the in-phase axis for the signal vector and a calculation the current signal-to-noise ratio based on statistical characteristics of the angle. The device includes a quadrature mixer and units of estimation signal-to-noise ratio. However, this method and device produce considerable errors, in particular, with small signal-to-noise ratios that are connected with different distribution laws, i.e., other than the Gaussian law for quadrature components.
The objective of the present invention is to address the drawbacks of known technical solutions.